pictures in Activity Stream

In a users activity stream, it shows the posts that the user has submitted. For each post, it is getting an image from the post. Problem here is some of the content that I use on my site comes from an external provider and it has a 1×1 pixel image used for tracking.

As a result, on the users activity stream, its using that image as the thumbnail of the post.

How can I change this so that it will always get the featured image on the post and not an image within the post itself?